ABSTRACT The long-term goal of this project is to elucidate the role, regulation and therapeutic potential of sphingomyelin synthase (SMS) in cancer. The current proposal focuses on the function of SMS1 in growth of GATA1 positive leukemic cells (in particular, erythroblasts and megakaryoblasts) and on SMS1 as a potential novel therapeutic target in acute myeloid leukemias (AML) that are enriched in such malignant immature populations (particularly M6 and M7 AML). SMS represents a class of lipid-metabolizing enzymes that consumes ceramide and produces diacylglycerol (DAG), two critical bioactive lipids with opposing functions in the control of key cellular processes often dysregulated during transformation, including proliferation, apoptosis, and differentiation. Thus, SMS may be linked to cancer, but knowledge on SMS regulation and downstream functions is limited. We previously showed that elevated expression of SMS1 is critical for proliferation of erythroleukemic K562 cells. Published and preliminary results also show that the elevated expression of SMS1 is a consequence of enhanced transcription occurring through a novel alternative promoter positively regulated by the transcription factor GATA1. Guided by gene expression data from the Cancer Cell Line Encyclopedia, we discovered that the highest SMS1 expression (mRNA and protein) in blood cancer cells is found in GATA1 positive AML blasts (erythroblasts and megakaryoblasts). Importantly, pharmacological and molecular inhibition of SMS1 in these leukemic cells revealed a critical role for SMS1 in proliferation and survival of these cells that is not observed in GATA1-negative AML blasts. Thus, based on these observations, we hypothesize that SMS1 is an important novel regulator of proliferation and maintenance of GATA1 positive AMLs and a potential novel target for improving the dismal therapeutic response of these leukemias. To address our hypothesis, we will: 1. Determine the role and function of SMS1 in GATA1 positive AML cells and 2. Establish SMS1 as a novel target for therapeutic intervention against GATA1 positive AMLs. Our proposal aims at establishing SMS1 as a novel critical regulator of GATA1+ AML cells and might provide a molecularly informed, and much needed novel therapeutic option for treatment of AML with erythroid or megakaryocytic enrichment.